Dumping

[Fred B]

Twin 350 marine power, slick behind boat. Not sure oil or gas?

 

[makomark]

or oil from the gear...??

More detail would help us that are not on the boat....age, hours, FWC or RWC, when do you see the "slick", etc.

 

[Boatyarddog]

Check your fluid levels.
Anything visible in the bilge?

 

[jendavis]

Look for any abnormalities or signs of leaks that could be causing the slick.